1. Field of the Invention
This invention is in the field of non-destructive testing of magnetizable workpieces wherein magnetic particles are used to detect the presence of seams and other imperfections. The specific improvement deals with the application of fluorescent magnetizable particles in the medium of a wax or resin type of aqueous emulsion thereby the film which deposits upon evaporation of the water holds the magnetizable particles in the flaw indication securely against the piece so that the workpiece can be handled roughly and still provide reasonably clear indications of imperfections.
2. Description of the Prior Art
Non-destructive testing procedures employing magnetic particles have been used for many years. More recently, the magnetic particles have been combined with fluorescent particles either in the form of a water or oil suspension, and the workpiece was inspected under filtered ultraviolet or black light to observe any concentration pattern of fluorescent particles caused by surface discontinuities. Prior art patents referring to this type of inspection technique include Switzer U.S. Pat. No. 2,267,999 and Kazenas U.S. Pat. No. 2,936,287. These patents relate, respectively, to lacquer bonded and resin bonded fluorescent magnetic particles for use in this type of inspection process.
Other prior art references which deal with the manufacture of the fluorescent coated magnetic particles, and the method of inspection using such particles are U.S. Pat. Nos. 3,404,093; 3,485,758; and 3,609,532, all assigned to the assignee of the present application.
The mganetic particle testing method is particularly applicable to the inspection of steel billets which are normally inspected in a continuous process in which the billet travels at relatively high velocity through a magnetizing yoke and through an applicator station where the fluorescent type magnetic particles are applied either in suspension or in dry form. It has been common practice to inspect such billets shortly after the magnetic particles were applied. Trained inspectors would thereupon mark any clusters of the magnetizable particles with a chalk or crayon, and leave the pieces for elimination of the defects either by scarfing or grinding.
Between the formation of the indication and the actual removal of the defective portion of the billet, the billet can be stored for an indefinite period of time, either indoors or outdoors. It may be moved more than once, and usually subject to very rough handling by bouncing along a roller conveyor, being pushed into a storage rack, or being picked up with electromagnets and then dropped into another location. Any indication that is not firmly fixed to the workpiece will no longer be visible after such rough handling.